Following elucidation of the regulation of the lactose operon in Escherichia coli, studies on the metabolism of many sugars were initiated in the early 1960s. The catabolic pathways of D-gluconate and of the two hexuronates, D-glucuronate and D-galacturonate, were investigated. The post genomic era has renewed interest in the study of these sugar acids and allowed the complete characterization of the D-gluconate pathway and the discovery of the catabolic pathways for L-idonate, D-glucarate, galactarate, and ketogluconates. Among the various sugar acids that are utilized as sole carbon and energy sources to support growth of E. coli, galacturonate, glucuronate, and gluconate were shown to play an important role in the colonization of the mammalian large intestine. In the case of sugar acid degradation, the regulators often mediate negative control and are inactivated by interaction with a specific inducer, which is either the substrate or an intermediate of the catabolism. These regulators coordinate the synthesis of all the proteins involved in the same pathway and, in some cases, exert crosspathway control between related catabolic pathways. This is particularly well illustrated in the case of hexuronide and hexuronate catabolism. The structural genes encoding the different steps of hexuronate catabolism were identified by analysis of numerous mutants affected for growth with galacturonate or glucuronate. E. coli is able to use the diacid sugars D-glucarate and galactarate (an achiral compound) as sole carbon source for growth. Pyruvate and 2-phosphoglycerate are the final products of the D-glucarate/galactarate catabolism.

7.Wilson KJ, Hughes SG, Jefferson RA. 1992. The Escherichia coli gus operon: induction and expression of the gus operon in E. coli and the occurrence and use of gus in other bacteria, p 7–22. In Gallagher SR (ed), GUS Protocols: Using the GUS Gene as a Reporter of Gene Expression. Academic Press, Inc., San Diego, Calif.

49.Hugouvieux-Cotte-Pattat N, Robert-Baudouy J. 1981. Isolation of fusions between the lac genes and several genes of the exu regulon: analysis of their regulation, determination of the transcription direction of the uxaC-uxaA operon, in Escherichia coli K-12. Mol Gen Genet182:279–287. [CrossRef]

65.Ritzenthaler P, Mata-Gilsinger M. 1982. Use of in vitro gene fusions to study the exuR regulatory gene in Escherichia coli K-12: direction of transcription and regulation of its expression. J Bacteriol50:1040–1047.

Following elucidation of the regulation of the lactose operon in Escherichia coli, studies on the metabolism of many sugars were initiated in the early 1960s. The catabolic pathways of D-gluconate and of the two hexuronates, D-glucuronate and D-galacturonate, were investigated. The post genomic era has renewed interest in the study of these sugar acids and allowed the complete characterization of the D-gluconate pathway and the discovery of the catabolic pathways for L-idonate, D-glucarate, galactarate, and ketogluconates. Among the various sugar acids that are utilized as sole carbon and energy sources to support growth of E. coli, galacturonate, glucuronate, and gluconate were shown to play an important role in the colonization of the mammalian large intestine. In the case of sugar acid degradation, the regulators often mediate negative control and are inactivated by interaction with a specific inducer, which is either the substrate or an intermediate of the catabolism. These regulators coordinate the synthesis of all the proteins involved in the same pathway and, in some cases, exert crosspathway control between related catabolic pathways. This is particularly well illustrated in the case of hexuronide and hexuronate catabolism. The structural genes encoding the different steps of hexuronate catabolism were identified by analysis of numerous mutants affected for growth with galacturonate or glucuronate. E. coli is able to use the diacid sugars D-glucarate and galactarate (an achiral compound) as sole carbon source for growth. Pyruvate and 2-phosphoglycerate are the final products of the D-glucarate/galactarate catabolism.

Genetic organization of sugar acid operons with their cognate regulatory circuits. Numbers refer to the position (min) of genes on the chromosome. The direction of the genes (represented by large arrows) shows their orientation on the bacterial chromosome (either clockwise or counterclockwise). The thin arrows represent the transcriptional effects of the regulators, with plain lines and broken lines to indicate primary and secondary levels of control, respectively. The + and – signs indicate positive and negative controls, respectively.

ecosalplus/1/1/3.4.2_fig_002_thmb.gif

ecosalplus/1/1/3.4.2_fig_002.gif

Figure 2

Genetic organization of sugar acid operons with their cognate regulatory circuits. Numbers refer to the position (min) of genes on the chromosome. The direction of the genes (represented by large arrows) shows their orientation on the bacterial chromosome (either clockwise or counterclockwise). The thin arrows represent the transcriptional effects of the regulators, with plain lines and broken lines to indicate primary and secondary levels of control, respectively. The + and – signs indicate positive and negative controls, respectively.